<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>Document</title>
</head>

<body>
  <div id="app">
    <span v-if="type==='username'">
        <label for="username">用户账号</label>
        <input type="text" placeholder="用户账号" key="username" />
      </span>
    <span v-else>
        <label for="email">用户邮箱</label>
        <input type="text" placeholder="用户邮箱" key="email" />
      </span>
    <button @click="btnClick">切换类型</button>
  </div>
  <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
  <script>
    const app = new Vue({
      el: "#app",
      data: {
        message: "hello",
        type: "username",
      },
      methods: {
        btnClick() {
          if (this.type === "username") {
            this.type = "email";
          } else {
            this.type = "username";
          }
        },
      },
    });
  </script>
</body>

</html>